A group of North Korean soldiers disguised as "indigenous people" of Russia's Far East have engaged in combat with Ukrainian troops in Russia's western border region of Kursk, according to a Ukrainian news report.

Citing Kyiv's top military officer, RBC Ukraine on Sunday reported that more than 11,000 North Korean soldiers are already stationed in the Kursk region and have taken part in battles against Ukrainian troops.

"These are mostly general military units. They are disguised as indigenous people of the Far East. They have the appropriate documents," Anatolii Barhylevych, the chief of the General Staff of the Armed Forces of Ukraine, was quoted as saying.

"They are trained to conduct operations in the European part," he added.

The report comes amid growing security concerns over military cooperation between North Korea and Russia, with South Korean and US officials confirming that the North has sent more than 10,000 troops to Russia in support of its invasion of Ukraine.

Last week, Seoul's spy agency said North Korean troops are believed to have been assigned to Moscow's airborne brigade and marine corps, with some of them already entering combat following local adjustment training.

The National Intelligence Service (NIS) also noted that North Korean troops, having entered combat, may have suffered casualties or injuries, adding that efforts are underway to determine the details of the combat circumstances and the extent of the damage.

On Sunday, the NIS said it is closely investigating intelligence that casualties have occurred among North Korean troops, marking its first confirmation of such a development.

RBC Ukraine earlier reported that about 500 North Korean soldiers were killed "as a result of the Storm Shadow missile strike on the Kursk region," citing Global Defense Corp., a defense news publisher. (Yonhap)